Microstructural Developments in Advanced High Strength Steels

For automotive applications, steel is mainly used for load bearing applications. Thus, the key mechanical properties of advanced high strength steels are strength and ductility. There are three types of advanced high strength steels that are of current interest: (i) dual phase steels, which have a microstructure comprised of a ferrite matrix with a martensite second phase; (ii) transformation induced plasticity (TRIP) steels, which are comprised of ferrite, bainite and retained (metastable) austenite; (iii) multi-phase steels, which can have all of the above microstructural constituents. In this paper, the following developments in AHSS are described: (i) fine-grained dual phase steels; (ii) aluminum alloyed TRIP steels; (iii) sub-critically annealed, cold rolled TRIP steels; (iv) strength and ductility mechanisms of TRIP steels; (v) welding of advanced high strength steels.